This invention relates generally to improved process and apparatus for assembling coils in the slots of stators or the like and more particularly to the insertion of overlapping coils during a single pass of the coil inserting apparatus.
As is known in the art, a dynamoelectric machine stator may comprise a slotted core of magnetic material having an axially extending rotor accepting bore therethrough and having a plurality of coils of conductive wire disposed in the slots with the coils between slots at either end of the core in end turn regions with certain ones of the coils being interconnected to form pole coil groups and those pole coil groups interconnected to form stator windings. Frequently both start and main windings will be provided with the start windings being electrically and/or physically displaced from the run windings to provide starting torque for the dynamoelectric machines. For example, an N-pole stator might typically have N main pole coil groups and N start pole coil groups with each of the start groups overlapping adjacent pairs of main groups. Such a stator may be provided with windings by forming those windings on coil forms, transferring the windings to a coil insertion device and displacing the windings from the coil insertion device into the stator slots.
Apparatus for inserting pre-wound coils into stator cores is well known in the art and represented for example, by U.S. Pat. Nos. 2,432,267 to Adamson and 3,324,536 to Hill. In using such apparatus to insert for example, in a first pass, a main winding, and in a subsequent pass, a start winding some difficulty may be experienced due to the lack of adequate space in the core for the second winding and for example, U.S. Pat. No. 3,402,462 to Walker et al teaches an ironing tool which is passed through the stator ahead of the second coil to force the first or main coil outwardly providing adequate slot space for the subsequent coil. A somewhat different approach is illustrated in U.S. Pat. No. 3,507,029 to Stuckey et al, which teaches a system for forming the rear end turns of the first coil radially outwardly to provide clearance for the subsequent insertion of additional coils into the slots of the stator core. Improved insertion of pre-wound coils employing machines of the type disclosed in the aforementioned Hill patent may also be achieved by modifying the movable stripper, which carries the coils into the stator core slots, in the manner taught in the U.S. Pat. No. 3,685,118 to Payne et al, or by attaching certain of the normally fixed upstanding blades or fingers which mesh with stator core teeth to the movable stripper as taught in U.S. Pat. No. 3,689,976 to Donavan. It is also known in the prior art to simultaneously insert both the main and start windings for example, in the manner taught in U.S. Pat. Nos. 3,625,261 to Hill et al and 3,845,548 to Arnold, and to move the main winding into the slots somewhat ahead of the start winding by using a riser above the normal stripper which engages only the main winding.
In the simultaneous or contemporaneous insertion of main and start windings the stripper pushes against the lower or inner winding which is generally the start winding and the upper or leading winding rides on the lower winding during insertion. Frictional forces on the upper winding as well as the lower winding accumulate and may tend to flatten the lower winding, particularly the lower portions thereof, spreading the blades or fingers and possibly locking up and damaging the equipment or the wires. Further the leading winding comes to rest in the stator core while the following or lower winding has an additional distance to travel and frictional forces exerted on it by the upper or outer winding, and particularly the lower end turns thereof, may be sufficient to break the wire or impair insertion. Bore insulating wedges typically accompany the inner winding during insertion and their placement may similarly be impaired.
Still further, a problem in both contemporaneous and sequential insertion of windings is that of locking wire size. When the ratio of wire diameter to blade gap is in the range of approximately 55% to 78% the relatively soft wire tends to deform slightly and act as a wedge with its adjacent wire. This wedging or nesting action produces side forces perpendicular to the blade surfaces which result in retarding frictional forces to the inserting process. Each wire in the coil will react in this manner and since the stripper is located at, and pushing from the bottom of the stack of wire, the frictional forces developed are cumulative. This is due to the fact that each wire develops it's own frictional force and must at the same time overcome the frictional retarding force of the wire directly above it. These accumulated forces present a retarding force at the stripper and for large numbers of turns may materially damage the wires directly adjacent or close to the stripper.
It is accordingly one object of the present invention to obviate one or more of the aforementioned problems.
Another object of the present invention is to improve the process of insertion employing machines of the type disclosed in the aforementioned Hill and Hill et al patents.
A further object of the present invention is to provide for the simultaneous insertion of main and start windings with reduced probability of damage to either the inserting equipment or the end product.